There are some pretty high voltages going to those bulbs. I worked at a convience store and I was changing a bulb in the freezer door, I touched the terminal and got a pretty good shock, I was frozen for atleast 2 seconds.
I dont know if it can be done, but just be careful.
Yes, the wires to a fluorecent light can be extended.
Have a look at the light for an aquarium, that has wires extending about 3 feet from the starter unit.
There will be mains voltage on the cable, BE SAFE, keep it well insulated.
It's not that high a frequency, it doesn't make any difference - we've just fitted electronic ballasts on a number of signs on the shop where I work, the tubes vary between two and three feet from the ballasts - and by definition, with an eight foot tube it's going to be a minimum of 4 feet from each end :lol:
The only problem I can see would be the tubes may not start as easily if their is no grounded metal ( like the reflector ) physically close to them. This depends on the tube though, and the ballast circuit, and is only needed for starting.